title: Prolonged signaling at the parathyroid hormone receptor by peptide ligands targeted to a specific receptor conformation.
abstract: The parathyroid hormone receptor (PTHR) is a class B G protein-coupled receptor that plays critical roles in bone and mineral ion metabolism. Ligand binding to the PTHR involves interactions to both the amino-terminal extracellular (N) domain, and transmembrane/extracellular loop, or juxtamembrane (J) regions of the receptor. Recently, we found that PTH(1-34), but not PTH-related protein, PTHrP(1-36), or M-PTH(1-14) (M = Ala/Aib(1),Aib(3),Gln(10),Har(11),Ala(12),Trp(14),Arg(19)), binds to the PTHR in a largely GTPgammaS-resistant fashion, suggesting selective binding to a novel, high-affinity conformation (R(0)), distinct from the GTPgammaS-sensitive conformation (RG). We examined the effects in vitro and in vivo of introducing the M substitutions, which enhance interaction to the J domain, into PTH analogs extended C-terminally to incorporate residues involved in the N domain interaction. As compared with PTH(1-34), M-PTH(1-28) and M-PTH(1-34) bound to R(0) with higher affinity, produced more sustained cAMP responses in cells, formed more stable complexes with the PTHR in FRET and subcellular localization assays, and induced more prolonged calcemic and phosphate responses in mice. Moreover, after 2 weeks of daily injection in mice, M-PTH(1-34) induced larger increases in trabecular bone volume and greater increases in cortical bone turnover, than did PTH(1-34). Thus, the putative R(0) PTHR conformation can form highly stable complexes with certain PTH ligand analogs and thereby mediate surprisingly prolonged signaling responses in bone and/or kidney PTH target cells. Controlling, via ligand analog design, the selectivity with which a PTH ligand binds to R(0), versus RG, may be a strategy for optimizing signaling duration time, and hence therapeutic efficacy, of PTHR agonist ligands.
authors.affiliation: Endocrine Unit and Center for Systems Biology, Massachusetts General Hospital, and Orthopedic Biomechanic Laboratory, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02114, USA.
authors.forename: Makoto
authors.initials: M
authors.lastname: Okazaki
authors.forename: Sebastien
authors.initials: S
authors.lastname: Ferrandon
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Vilardaga
authors.forename: Mary L
authors.initials: ML
authors.lastname: Bouxsein
authors.forename: John T
authors.initials: JT
authors.lastname: Potts
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Gardella
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000502:physiology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006801:Humans; D007668:Kidney / Q000502:physiology; D008024:Ligands; D051379:Mice; D010455:Peptides / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051381:Rats; D044168:Receptor, Parathyroid Hormone, Type 1 / Q000737:chemistry* / Q000378:metabolism*; D015398:Signal Transduction; D013997:Time Factors
chemical_list: D008024:Ligands; D010455:Peptides; D044168:Receptor, Parathyroid Hormone, Type 1; D016244:Guanosine 5'-O-(3-Thiotriphosphate)